a. Field of the Invention
The instant invention is directed toward an electrode catheter and a method for using the electrode catheter for tissue mapping, guidance and/or tissue ablation. In particular, the electrode catheter of the present invention may assess electrode location relative to an insertion sheath and/or assess electrode-tissue contact.
b. Background Art
Catheters have been in use for medical procedures for many years. Catheters can be used for medical procedures to examine, diagnose, and treat while positioned at a specific location within the body that is otherwise inaccessible without more invasive procedures. During these procedures a catheter is typically inserted into a vessel near the surface of the body and is guided to a specific location within the body for examination, diagnosis, and treatment. For example, catheters can be used to convey an electrical stimulus to a selected location within the human body, e.g., for tissue ablation. In addition, catheters with sensing electrodes can be used to monitor various forms of electrical activity in the human body, e.g., for electrical mapping.
Catheters are used increasingly for medical procedures involving the human heart. Typically, the catheter is inserted in an artery or vein in the leg, neck, or arm of the patient and threaded, sometimes with the aid of a guide wire or introducer, through the vessels until a distal tip of the catheter reaches the desired location for the medical procedure in the heart. In the normal heart, contraction and relaxation of the heart muscle (myocardium) takes place in an organized fashion as electro-chemical signals pass sequentially through the myocardium.
Sometimes abnormal rhythms occur in the heart, which are referred to generally as arrhythmia. The cause of such arrhythmia is generally believed to be the existence of an anomalous conduction pathway or pathways that bypass the normal conduction system. These pathways are usually located in the fibrous tissue that connects the atrium and the ventricle.
An increasingly common medical procedure for the treatment of certain types of cardiac arrhythmia is catheter ablation. During conventional catheter ablation procedures, an energy source is placed in contact with cardiac tissue (e.g., associated with a anomalous conduction pathway) to heat the tissue and create a permanent scar or lesion that is electrically inactive or noncontractile. The lesion partially or completely blocks the stray electrical signals to lessen or eliminate arrhythmia.
Ablation of a specific location within the heart requires the precise placement of the ablation catheter within the heart. Precise positioning of the ablation catheter is especially difficult because of the physiology of the heart, particularly because the heart continues to beat throughout the ablation procedures. Commonly, the choice of placement of the catheter is determined by a combination of electrophysiological guidance and computer generated maps/models that may be generated during a mapping procedure. Accordingly, it is desirable that any map or model of the heart be as accurate as practicable.
Several difficulties may be encountered, however, when attempting to form lesions at specific locations using some existing ablation electrodes. One such difficulty encountered with existing ablation electrodes is how to ensure adequate tissue contact and/or electrical coupling. Electrode-tissue contact is not readily determined using conventional techniques such as fluoroscopy. Instead, the physician determines electrode-tissue contact based on his/her experience using the electrode catheter. Such experience only comes with time, and may be quickly lost if the physician does not use the electrode catheter on a regular basis. In addition, attempts to directly measure contact between an electrode and target tissue are often subject to local variations in the surrounding media. Such variation can distort such measurement, which can lead to false electrode-tissue contact indications.